The spring resets itself incorrectly... Parts are
Modify tappet, nozzle, selector plate, cutoff lever
G&P cylinder and cylinder head, trigger set, anti-reversal
XYT gears and safety switch.
When I had a DBoys spring it worked fine, but that is unusable because it shoots through the outer ring of the bottom of a pop can.
I don't recall having heard of something like this... But then again the only other mechbox I had was a V3, so what do I know...
YouTube - G&P mechbox problem